Firemen and rescue teams must perform activities under very difficult environmental conditions in fires or other dangerous situations. Harmful gases, e.g., toxic or explosive gases, may be present in the breathing air. It is known in this connection that the concentration of the harmful gases in the breathing air can be determined by means of a gas-measuring device and the person can be warned when limit values of the harmful gas are exceeded in the dangerous situation.
Firemen and rescue teams are subject to overstimulation and considerable physical as well as psychological stress during the dangerous situations. Weak warning signals or warning signals that are difficult to recognize are therefore usually not perceived by the rescue teams. For example, simple warning lights on stationary or portable gas-measuring devices are, in general, not sufficient, because the warning lights cannot be recognized any longer even at a short distance, especially in case of low visibility due to the intense generation of smoke. Acoustic warning means are not detected any longer because of high noise levels, either.
DE 10 2005 045 272 B4 and DE 101 40 945 B4 show gas-measuring devices for detecting harmful gases in the air. In general, a gas-measuring device with one or more sensors, which are provided for measuring the expected gas concentration and whose measuring sensitivity is selected correspondingly, is used to measure a gas sample. The gas-measuring device has, as a rule, an analysis unit, which analyzes the measured signals of the sensors. The analysis unit checks whether the measured signals exceed a previously defined and preset limit value. In case the limit value is possibly exceeded or in case of implausible measured values, the user is usually warned optically, mechanical or acoustically.
Portable gas-measuring devices are carried by users or the person in dangerous situations as personal monitoring devices in order to rapidly detect harmful gases in the working area and to warn the user. Based on the mobility of the portable gas-measuring device, the gas-measuring device must have the most compact housing dimensions possible. This means that only a limited surface is available for generating warning stimuli, especially in case of an optical alarm by means of light, so that the user cannot, in general, perceive the warning stimulus under difficult environmental conditions.
Stationary and quasistationary gas-measuring devices have a longer operating time due to better power supply. The housing dimensions are of secondary importance. In contrast, there is, in general, no possibility for individually alarming the user.